At a recent conference in England, a group of fully-grown adults played a strange game of telephone. They sat quietly, passing papers down the line, each person working quickly but carefully. But the strangest part wasn’t that adults were playing a children’s game, or that they were writing instead of whispering. It’s that they weren’t using real languages.

These people have invented their own languages, called conlangs, and this game is actually a test. Each person’s task is simple: Translate a passage from another person’s conlang into their own, then pass it along. The last person translates it back to English. If the text is the same then they’ve all passed the test. Otherwise, as in childhood telephone, they end up with ridiculous results.

Fantasy movies and TV shows are increasingly enlisting conlangers to invent languages as part of the effort to build more immersive fantasy worlds. Historically, though, conlangs haven’t been so popular. The Ewoks in Star Wars spoke in silly nonsense noises, but today, fully fleshed out conlangs are all but essential for blockbuster movies like Avatar and hit TV shows like Game of Thrones.

Producers like David Benioff and Dan Weiss, executive producers for Game of Thrones, have said that conlangs add depth to characters and quite simply sound more realistic than the nonsense noises featured in older films and TV shows.

Linguists agree. “I think you can tell the difference,” says Arika Okrent, a trained psycholinguist — someone who studies the psychology of language — and author of In the Land of Invented Languages. She says you have to listen closely to what the characters are saying, but that you can tell when the noises are just nonsense.

And she’s not alone. David Peterson, one of the only conlangers to parlay the hobby into a profession, says he agrees. Even as a child, he says he knew that the alien languages in Star Wars made no sense. Today, Peterson is well known for the languages he has invented for shows like Game of Thrones and Defiance, as well as for films like Thor: The Dark World.

But Okrent says it’s possible that only certain people, like trained linguists, can notice right away. Okrent and Peterson may be more attuned to how languages sound because they study them in depth, and are therefore uniquely able to distinguish conlangs and real languages from nonsense.

But to the untrained ear, nonsense noises can certainly sound like a language — just listen to someone double-talking. Double-talking is a talent in which the speaker mimics how foreign languages sound, without actually saying any real words.

Listening to a double-talker is a bizarre experience, especially if the person is mimicking your native language. Take Sara Forsberg, a YouTuber who double-talks in a dozen different languages. She chats as if having a casual conversation with a friend, but the noises she’s making only sound like real words. Maybe that’s why her video What Languages Sound Like to Foreigners has over 15 million views.

The video may be beguiling, but you might not be so amused if your native tongue were mistaken for nonsense. That’s what happened to Rita Quintero, an indigenous woman from Mexico who found herself institutionalized in Kansas because the locals misinterpreted her Tarahumara language for schizophrenic babbling. She spent 12 years taking antipsychotics that she didn’t need until 1992, when an advocacy group finally identified the language she was speaking.

Uninformed listeners may mistake double-talking for a language, while failing to recognize Tarahumara as real. Double-talk is so effective because it plays off our preconceived notions of what certain languages sound like, but that only works if the listener is already familiar with the language being mimicked. Indigenous languages, like Tarahumara, may use sounds that are completely unfamiliar to people who mostly hear European languages. That unfamiliarity makes certain real languages sound fake because they don’t sound like any language the listener is used to hearing.

Languages that an audience is very familiar with also come with preconceived notions, about both how the language sounds and what type of person speaks it. American producers, for instance, are influenced by the cultural stereotypes that most Americans are familiar with, says Peterson. He says the hard “ch” sound in German seems harsh to Americans, so conlangs with that sound signal to viewers that the speaker is a quintessential bad guy.

But conlangs do more than provide a simple stereotype. They’re an integral part of building a truly immersive world, says Christophe Grandsire-Koevoets, president of the Language Creation Society. “Audiences want to have the impression that there’s actually a world out there,” he says. The Language Creation Society, founded by Peterson, is a group meant to help conlangers invent and share their languages.

Many conlangers create their conlang first and then develop characters based on that language, says Grandsire-Koevoets. J.R.R. Tolkien is famous for his elaborate languages, which he designed purely for his own enjoyment, and the world of Lord of the Rings and The Hobbit flowed from those languages. And once he designed a conlang, he never stopped evolving it.

Today in Hollywood, conlangers do the opposite, and mold their created languages to fit into a fictional culture that already exists. But whether the language or the culture comes first, the two are nearly inextricable.

Cognitive science studies seem to confirm that language is linked to the way certain cultures perceive the world. People who speak languages with gendered nouns, for example, describe certain objects differently based on the assigned gender. The word bridge is feminine in German, but masculine in Spanish. So when researchers asked native speakers to associate adjectives with bridges, Germans used feminine words like slender, elegant and pretty, while Spanish speakers used masculine words like sturdy, big and strong. The opposite was true for key, which is masculine in German and feminine in Spanish — Germans described keys as more masculine than did Spanish speakers.

Conlangers similarly use grammatical structures like gender to express certain cultural views. Margaret Ransdell-Green, a lifelong conlanger and linguist-in-training, uses gendered words to express how her invented people see real-world genders. Their society is strongly matriarchal, so their language uses gender-specific titles that honor and respect women, and only use them for particularly exalted men.

More broadly, conlangers use vocabulary to illustrate the practical aspects of a culture. When Peterson invented Dothraki for Game of Thrones, he says he thought through every detail about the Dothraki world — what they wear, where they go, and what they do. For instance, he says the Dothraki discuss distance based on how far a horse can travel at a particular speed before it gets tired and has to walk. That small fact provides a sense of the culture as a whole: The Dothraki value horses enormously, so their lexicon values them as well. Peterson says he puts a lot of effort into these details because they’re simple ways to insert cultural values into a conlang.

Real languages contain these details as well, though they’re artifacts of a language and a culture developing together over time. Europeans in the Middle Ages, for instance, depended on agriculture and used beasts of labor to help tend their crops. Farming culture helped dictate the lexicon back then, so words developed over time that helped people navigate that world. Today we have a word to designate the amount of land that can be ploughed in one day by a pair of oxen: an acre. Although English speakers don’t use acre in that sense anymore, the word reflects how the culture of English speakers developed.

Peterson says he never used to take details like this into account when he made his early conlangs. It was only through working with other conlangers that he improved, and he says the best work is still done by people you’ve never heard about — by people playing their strange game of telephone. That culture of conlangers, strange as it may be, is really what helped Peterson learn how to create the culture of his conlangs. “I didn’t understand at that time how closely intertwined language and culture were. As soon as you create words, you create culture.”